R M Cullen MD MSc MFM BA DipStats DipProfEthics

june 2015

Not all babies should be vaccinated against pertussis

Mass vaccination against whooping cough has increased the burden of disease in under one year olds, rather than halving it as was the aim. The vaccine confers short term protection against the disease when compared to the long lasting, possibly lifelong immunity which follows natural infection. As a result babies are now exposed to the contagion from siblings, parents, and social contacts who would never have been coughing if they had not been vaccinated themselves as babies.

This is simple stuff. It was new and highly controversial when Dr Wayne Walker and I first pointed it out in the last years of the last century. But that debate is over. Way back then, in 1997, we did something very simple. In order to establish what the impact of mass vaccination, which commenced in 1960, had been we looked at hospital discharge data from 1950 to 1996. To our surprise we found a forty per-cent increase in hospital admissions by the 1990s compared to the pre-vaccination era.

Because of the unexpected findings I presented the work to a group of public health specialists and trainees at a seminar, after our paper had been peer reviewed and accepted for publication. Someone in the audience forwarded a pre-print to the Ministry of Health in Wellington and pressure was put on the journal editor to pull the paper. It was a close call, but in the end the Ministry had to be satisfied with space to respond in a subsequent issue.

The data are no longer controversial. Our work has been repeated and the accepted wisdom is that by the 1990s hospital admission rates were twice what they had been in the 1960s. In the following decade admission rates fell by twenty percent. It is unclear whether this reflects a true decline or a much smaller than expected epidemic in 2009, which has been followed by a much bigger than expected epidemic in 2013.

In the 1960s fewer babies were infected with pertussis. The pool of susceptibles was smaller, as mass vaccination had provided many babies with immunity, at least for seven years or so. The siblings, parents, grandparents and social contacts of unimmunized babies were immune, having long lasting immunity from natural infection, so there were few opportunities for babies to be exposed to whooping cough.

By the 1990s things had changed. Vaccine coverage was modest. A major survey in 1992 showed that only sixty percent of children had received their vaccinations by age two. The babies vaccinated in the 1960s and 1970s were parents, or even grandparents in the 1990s. Although there were fewer babies to infect than in the 1950s, those babies were exposed to many more sources of infection. The result was the increase in hospital admissions we reported.

In our 1997 paper we suggested the obvious. It was important to increase the number of babies immunised on time. This has been done. We also suggested booster shots could be given to parents, siblings, and even grandparents. It took ten or fifteen years, but this is now accepted.

We also suggested that population wide mass vaccination in the summer before an epidemic was expected might prevent an epidemic from occurring.

In 2000 the Ministry of Health replaced the vaccine it was using with a less effective one which conferred even more temporary immunity. The rationale was that the less effective vaccine had fewer side effects.

However, what we did not talk about in 1997 was how the burden of disease could be reduced to pre-vaccination levels. How might the harm done by mass vaccination be reversed?

The problem today is a vaccine problem. There is not much more to gain by trying to mop up the last of the unvaccinated babies. It is unlikely that any senior doctor or any Ministry official will acknowledge this publicly, but that’s the truth of the matter.

The choice parents face is whether to vaccinate their baby with a vaccine that is fairly effective but which provides protection for only a few years, or whether to leave their baby unvaccinated against whooping cough. Unvaccinated babies can be protected from infection by ensuring they are not exposed to people with a cough. They should stay at home until they can crawl. Their social contacts can be given booster doses.

The effect of choosing not to vaccinate against pertussis is that the child will be infected naturally, if all goes well at age three or older. She or he will have long lasting immunity and will not infect younger brothers or sisters when they come along. Nor will he or she infect their own children.

This is a risk balancing exercise. If home is uncrowded and warm, if baby is born in spring or summer, if diet is good, if baby can be kept away from anyone with a cough, and if social contacts receive booster doses, then the risk of contracting whooping cough before age one is minimised. It is not nil, and pertussis is a nasty illness in the very young.

A parent who chooses to forego pertussis immunisation is faced with the further issue that pertussis is bundled together in the one injection with vaccines for polio, tetanus, diphtheria, hepatitis B and Haemophilus influenzae type B. Reject one, reject them all.

If the goal is to reduce the burden of disease, not just in the very young, but in the whole population, then the parents of those babies least likely to be hospitalised with whooping cough should decline this vaccine.

Here's a more recent reference than our 1997 work

https://www.auckland.ac.nz/en/about/news-events-and-notices/news/news-2012/2012/08/13/Whooping-cough-admission-rates-cut-by-a-fifth.html